1. Field of the Invention
The present invention relates to a switch having a housing that has a lower housing part as the first housing part and an upper part, closing off the lower housing part, as the second housing part; and having a temperature-dependent switching mechanism, introduced into the lower housing part, for which a first countercontact is provided on an inner base of the upper part and a second countercontact is provided on an inner base of the lower housing part; such that the switching mechanism creates, as a function of its temperature, an electrically conductive connection between the two countercontacts, to which contact can be made from outside through the associated housing part, and at least one housing part is made of insulating material.
2. Description of Prior Art
A switch of this kind is known from DE 37 10 672.
In the case of the known switch, the housing has a cup-like lower housing part made of electrically conductive material as well as a cover part, closing off the lower housing part, that is made of insulating material. The switching mechanism, which comprises a spring disk that carries a movable contact, is introduced loose into this housing. The spring disk operates against a bimetallic disk that is slipped over the electrical contact. Below the switching temperature the spring disk, which is braced against the base of the lower housing part, presses the movable contact against a countercontact that is provided on the inside of the cover and extends outward, in the manner of a rivet, through the wall of the cover.
Since the spring disk itself is made of electrically conductive material, below the response temperature of the switching mechanism it provides a low-resistance electrically conductive connection between the countercontact on the cover part and the lower housing part, to which contact is made from outside. If the temperature of the switching mechanism is then increased, the bimetallic disk suddenly snaps over and pushes the movable contact, against the force of the spring disk, away from the countercontact on the cover, so that the electrical connection is opened.
Switches of this kind are commonly used for temperature monitoring of electrical devices. As long as the temperature of the electrical device does not exceed a predetermined response temperature, the switch, which for this purpose is connected in series with the load being protected, remains closed. If the temperature of the load then increases excessively, the bimetallic disk snaps over and thus interrupts the flow of current to the load.
It is a disadvantage of the known switch that it is relatively complex to produce. This is due principally to the fact that after production of the cover part, the countercontact must then be fastened onto the cover part; at the same time, an electrically conductive connection out through the wall of the cover part must be provided. This is done in the manner of a rivet that transitions, outside the cover, into a head to which conductors, crimp terminals, etc. must be soldered. This assembly of the countercontact to the cover is generally performed manually, and is thus very cost-intensive.
With the known switch the connection technology is also complex, since after its final assembly is complete, conductors or crimp terminals must be soldered or welded both onto the rivet head and onto the electrically conductive lower housing part at a suitable point. This specific connection technology is, however, very cost-intensive, since it is often implemented by hand.
A further switch, in whose housing a switching mechanism as described above is also arranged, is known from DE 21 21 802 A. In this switch the cover part and lower housing part are both cup-shaped, and are made of electrically conductive material. One-piece crimp terminals are shaped onto the upper part and onto the lower housing part, the crimp terminal of the lower housing part extending outward through a corresponding cutout in the wall of the upper part. An insulating film is arranged between the upper part and the lower housing part in order to insulate the two housing parts electrically from one another.
The switching mechanism thus makes contact on the one hand with the housing lower part via the spring disk, and on the other hand with the cover part via the movable contact, so that an electrically conductive connection exists between the two crimp terminals as long as the temperature of the switching mechanism is below the response threshold. If the temperature of the switching mechanism rises, this electrical connection is opened in the manner described above.
Although the connection technology is very simple to implement with this known switch (conductors simply need to be clamped into the crimp terminals), its assembly is very complex due to the insulating film that must be introduced, and therefore can only be accomplished manually. This manual final assembly is not only wage-intensive, but also leads to assembly errors and thus to a higher reject rate.
A further switch with a lower housing part made of electrically conductive material and a cover part made of insulating material is known from DE 31 22 899 C2. In this switch two connector tongues are cast into the cover part. A first connector tongue is integrally joined to a plate-shaped element that sits in the center of the cover part and carries the first countercontact. The other contact tongue constitutes, together with a contact strip extending transversely, a T-shaped element whose outer ends are bent downward around the cover, where they are in contact (in the assembled state) with the lower housing part, the inner base of which serves as the second countercontact.
Introduced into the metallic lower housing part is a bimetallic switching mechanism which operates in the manner already described above.
With this switch the complex production of the cover part is disadvantageous: after the two connector tongues are cast in, the laterally projecting ends of the contact strip must be bent downward, which requires additional production steps. The known switch is moreover of complex design: during final assembly, it is important that the bent-over ends also in fact come into electrical contact with the lower housing part. A further disadvantage of this switch consists in the fact that further contact resistances are present between the lower housing part and the bent-over ends of the contact strip; these may corrode in everyday use, thus possibly having a negative influence on the function of this switch.
A further switch is known from WO 94/19815. This switch has a housing, made of PTC material, from which two connector tongues project laterally. In this case the temperature-dependent switching mechanism comprises a bimetallic tongue, clamped in at one end, that is joined at its clamped end to a first connector tongue and at its free end carries a movable contact which interacts with a connector element in the interior of the switch that can be configured integrally with the second connector tongue.
This switch is of entirely different construction from the generic switch; in it, for example, completely different demands are made on the bimetallic tongue, since in this case the switching mechanism cannot be introduced loose into the housing as is the case with the generic switch. Assembly of this switch is first of all difficult due to the complexity of introducing the bimetallic tongue in correct position and joining it to the first connector tongue, and also presents further problems associated with the fact that the housing is made of PTC material.